Traction vehicles such as, for example, locomotives, employ electric traction motors for driving wheels of the vehicles. In some of these vehicles, the motors are alternating current (AC) motors whose speed and power are controlled by varying the frequency and current of AC electric power supplied to the motors. Commonly, the electric power is supplied at some point in the vehicle system as direct current power and is thereafter inverted to AC power of controlled frequency and amplitude. The electric power may be derived from an on-board alternator driven by an internal combustion engine or may be obtained from a wayside power source such as a third rail or overhead catenary.
In conventional systems the power is inverted in a solid-state inverter incorporating a plurality of diodes and electronic switching devices. In a locomotive, large off-highway vehicle, or transit application, the traction motors may develop more than 1000 horsepower per motor, thus requiring very high power handling capability by the associated inverter. This, in turn, requires power semiconductor switching devices such as GTOs (gate turn-off thyristors) or IGBTs that are capable of controlling such high power and of dissipating significant heat developed in the semiconductor devices due to internal loss generating characteristics.
The power semiconductor devices are typically mounted on heat transfer devices such as heat sinks, which aid in transferring heat away from the semiconductor devices and thus preventing thermal failure of the devices. An electrical circuit area in which the semiconductor devices are located may include various control and timing circuits, including low power semiconductor devices, used in controlling switching of the power semiconductor devices.
In locomotives, an inverter drive system for large AC motor applications typically includes an inverter associated with each traction motor, such that a six-axle locomotive would have six inverters, each for powering a respective one of six traction motors connected to respective ones of the six axles. In such applications, a certain number of inverters and other components may be located on, and be accessible from, one side of the locomotive (referred to the “A side” of the locomotive), while the remainder of the inverters and other components are located on, and accessible from, the other side of the locomotive (referred to the “B side” of the locomotive). In such an arrangement, the inverters on opposing sides of the locomotive may be spaced apart by as much as five feet (1.5 m), defining an air plenum therebetween which allows for the necessary circulation of ventilation air for cooling purposes.
Existing methods of connecting the multiple inverters on opposed sides of the plenum involve the use of a solid bus connection between the inverters. In particular, a solid bus bar is typically arranged at the top of the envelope and spans the plenum at the top thereof to connect the opposed inverter arrays. Such a configuration, however, increases inductance between the inverters arranged on the A side of the locomotive and the inverters arranged on the B side of the locomotive, which may lead to an increase in undesirable circulating currents. In addition, this configuration increases the height of the inverter assembly/envelope as a whole, due to the clearance requirement for a solid bus, which can be problematic when attempting to meet locomotive height or clearance requirements.